Evidence of liquefaction during the 2017 Pohang earthquake has highlighted the urgent need to evaluate the current seismic design standard for liquefaction in Korea, particularly the liquefaction triggering standard. With the simplified method, which is the most popular method for evaluating liquefaction triggering, the factor of safety for liquefaction triggering is calculated via the cyclic stress ratio (CSR) and the cyclic resistance ratio (CRR). The parameters in the CSR and CRR have undergone changes over time based on new research findings and lessons learned from liquefaction case-histories. Hence, the current design standard for liquefaction triggering evaluation in Korea should also reflect these changes to achieve seismic safety during future earthquakes. In this study, liquefaction susceptibility criteria were discussed initially and this was followed by a review of the current liquefaction triggering codes/guidelines in other countries and Korea. Next, the parameters associated with the CSR such as the maximum ground acceleration, stress reduction factor, magnitude scaling factor, and overburden correction factor were discussed in detail. Then, the evaluation of the CRR using the SPT N-value and CPT qc-value was elaborated along with overburden and clean-sand correction factors. Based on this review of liquefaction triggering evaluation standards, recommendations are made for improving the current seismic design standard related to liquefaction triggering in Korea.

Recently, some of the most destructive earthquakes have occurred in South Korea since earthquake observations began in 1978. In particular, the soil liquefactions have been reported in Pohang as a result of the ML 5.4 earthquake that occurred in November 2017. Liquefaction-induced ground deformations can cause significant damage to a wide range of buildings and infrastructures. Therefore, it is necessary to take practical steps to ensure safety during an earthquake. In the current seismic design in South Korea, the Hachinohe earthquake and Ofunato earthquake recorded in Japan, along with artificial earthquakes, have been generally used for input motions in dynamic analyses. However, such strong ground motions are only from Japan, and artificial earthquake ground motions are different from real ground motions. In this study, seven ground motions are selected, including those recorded in South Korea, while others are compatible to the current design spectra of South Korea. The effects of the newly selected ground motions on site response analyses and liquefaction analyses are evaluated.

국가기관과 기업은 정비사를 양성을 위한 고등학교부터 대학교, 기업 훈련센터 같은 교육기관을 만들어 숙련된 정비사로 훈련시키려고 많은 노력을 하고 있다. 하지만 교재를 이용한 이론교육과 현장에서 사용하지 않는 장비를 이용한 실습교육으로는 제대로 된 정비교육을 진행하지 못하며 특수 장비를 활용한 교육이나 위험한 상황을 가정한 정비의 교육은 매우 위험하여 영상이나 사진으로 교육을 진행하고 있었다. 최근에는 VR과 AR을 접목하여 단순정비에서 특수정비까지 시뮬레이션으로 안전하게 상황을 체험하고 문제를 해결하는 효과적인 교육 시뮬레이션이 연구되고 개발되는 사례가 많이 있다. 본 논문에서는 다누리 VR과 DisTi Engine, Remote AR을 비교분석하고, 유니티 엔진 기반으로 외부에서 전달된 정보를 기반으로 콘텐츠를 디바이스 화면에 최적화하여 출력하는 AR API 를 소개하고, VR 디바이스인 HTC Vive의 컨트롤러와 HMD의 정보를 실시간으로 수집하고 수집된 정보를 파일에 저장하는 VR API를 구현한 사례를 소개했다. 본 연구에서 구현한 API를 사용하면 콘텐츠를 제작할 때 도움을 줄 수 있을 것이다.

TiO2 nanoparticles were synthesized by a sol-gel process using titanium tetra isopropoxide as a precursor at room temperature. Ag-doped TiO2 nanoparticles were prepared by photoreduction of AgNO3 on TiO2 under UV light irradiation and calcinated at 400 oC. Ag-doped TiO2 nanoparticles were characterized for their structural and morphological properties by Xray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The photocatalytic properties of the TiO2 and Ag-doped TiO2 nanoparticles were evaluated according to the degree of photocatalytic degradation of gaseous benzene under UV and visible light irradiation. To estimate the rate of photolysis under UV (λ = 365 nm) and visible (λ ≥ 410 nm) light, the residual concentration of benzene was monitored by gas chromatography (GC). Both undoped/doped nanoparticles showed about 80 % of photolysis of benzene under UV light. However, under visible light irradiation Ag-doped TiO2 nanoparticles exhibited a photocatalytic reaction toward the photodegradation of benzene more efficient than that of bare TiO2. The enhanced photocatalytic reaction of Ag-doped TiO2 nanoparticles is attributed to the decrease in the activation energy and to the existence of Ag in the TiO2 host lattice, which increases the absorption capacity in the visible region by acting as an electron trapper and promotes charge separation of the photoinduced electrons (e−) and holes (h+). The use of Ag-doped TiO2 nanoparticles preserved the option of an environmentally benign photocatalytic reaction using visible light; These particles can be applicable to environmental cleaning applications.

In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at 470˚C, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.

본 논문에서는 내구성과 수명을 획기적으로 향상시키기 위해 제3세대 건설재료인 섬유강화 플라스틱(FRP) 소재로 제작된 사각형 중공 교량 바닥판의 파괴모드를 실험과 해석을 통해 분석하였다. 재하시험 결과 바닥판의 강축방향의 거동은 파괴 직전까지도 거의 선형탄성적으로 거동한 반면, 약축방향의 거동은 재하초기부터 작은 하중하에서도 큰 비선형성을 보였다. 이 약축방향 비선형성의 원인은 웨브와 플랜지 연결부의 불완전한 일체거동으로 인한 소성거동 때문인 것으로 판단된다. 웨브와 플랜지의 연결부에 소성힌지를 도입한 간단한 구조모델을 이용하여 이를 확인하였다. 접착부의 박리 파괴 가능성도 검토하였으나 이는 대상 중공바닥판의 약축방향 파괴에 직접적으로 관여하는 것은 아닌 것으로 판단된다 약축방향의 구조거동을 개선시키기 위한 방안으로 내부를 폼으로 충전하는 방법을 제시하였으며 그 가능성을 구조해석을 통해 확인하였다.